Well - Canon offers some weather sealed L lenses but those are pretty expensive and most of them (if not the big and heavy tele lenses) are made of plastic outside as well and they still have some glass inside. So in those rough conditions I'd rather think of an insurance than a special lens.

aside from the prime I mentioned earlier the canon 17-55 is usm could be interesting then, in so far that its not technically a parfocal lens, but based on my experience using it for video, it pretty well is. Parfocal means that as you zoom in and out things stay in focus. Obviously useful for video on a DSLR.

It also has IS, which would be useful like Jiko suggested. Its a good quality lens, possibly a bit big and heavy.

the other parfocal lenses, but without IS is the 16-35mm f/2.8L USM and EF 17-40mm f/4L USM and being L lenses should be a bit more robust.